EP0092036B1 - Device for heating electrically conductive bulk materials - Google Patents

Description

The invention relates to a device for the direct heating of electrically conductive bulk goods in a furnace space using the electrical heating resistance of the bulk material, with an inlet, an outlet and with intermediate, laterally delimiting pairs of opposite side walls and with at least two different on each other Level of the furnace chamber, arrangements one above the other, each consisting of at least one pair of electrodes lying opposite one another at the same height and attached to a pair of side walls of the furnace chamber.

It is known to heat carbon-containing raw materials in the manufacture of electrode masses for the electrodes of the electric melting furnace or electrolyte mass in the production of melt-electrolytic aluminum. As is known, in particular for the production of high-quality briquettes, the starting material, such as coke, soot, coal, is intimately mixed, then provided with a thermoplastic binder, in particular pitch, and then pressed. To adequately fill the molds, it is advisable to preheat the bulk material beforehand, and resistance-heated devices of the aforementioned type are used for this.

Electric furnaces are also known in which the current passes horizontally through carbon materials and is supplied by means of electrodes suspended from rollers, which are drawn out as the furnace fills upwards. An attempt was hereby made to heat the entire contents of the furnace as evenly as possible, but with the structure mentioned last, considerable mechanical outlay was provided with cumbersome precautions for the power supply. However, the heat was not distributed satisfactorily because a rest period of approximately 12 hours after filling was considered necessary.

A continuous furnace with annular electrodes is also known, in which the current is passed through the coke through a single flow path. Although this allows a smaller furnace cross-section to be selected, the filling is reduced with an excessive increase in the overall height, and continuous operation has not become established in practice because most processing machines do not work continuously but in batch mode. Intermediate buffers are extremely cumbersome and complex.

According to DE-PS 1 571 443, a resistance-heated furnace has therefore been provided to even out the heating, in the construction of which the transverse dimension of the current path decreases with increasing distance from the electrode, in order to thereby even out the current density over the entire furnace cross section. The disadvantage, however, is that a container with a frequency of Hz is produced, which is not only very expensive to manufacture, but also complicates the use of modern, temperature-resistant and wear-resistant materials, which are only supplied in certain standard formats, without making any significant changes. In particular, subsequent processing using conventional technology is hardly possible.

Like the present invention, US-A-771 250 relates to a device for the direct heating of electrically conductive bulk materials in a stovepipe with the features mentioned at the beginning. All electrodes of this device are galvanically coupled to one another via interconnected secondary windings of transformers. Just as with the device according to the already mentioned DE-PS 1 571 443, an attempt is also made in the device according to the above-mentioned US patent to bring about a uniform heating of the material in the furnace by means of a special arrangement and design of the electrodes. The known solution attempts have in common the disadvantage that in the case of unevenly piled bulk material and in particular because of the greater loading of the lower layers compared to the relatively loose upper layers, the contact resistances between the individual parts of the bulk material are different, so that this results in an uneven current distribution and accordingly uneven heating of the bulk material also results. This disadvantage cannot be completely avoided even by making the furnace space and the electrodes more complicated.

The invention is therefore based on the object to improve a device of the type mentioned in such a way that the bulk material can be heated uniformly and yet the geometric shape of the furnace space is as simple as possible, so that the use of commercially available materials is possible without special processing.

According to the invention, this object is achieved in that the pairs of electrodes arranged one above the other are connected such that one pair of electrodes is galvanically separated from the other pair of electrodes.

In this way, several, galvanically separated circuits are available, which enable a uniform introduction and distribution of the current in the bulk material to be heated. The respective pair of electrodes can have the same or different electrical potential, so that the one current path of one pair of electrodes hardly has any influence on that of the other pair of electrodes. The same applies to the use of a large number of pairs of electrodes. Not only is uniform heating of the bulk material achieved in this way, but also the current breakthroughs and the associated formation of channels with increased material temperature are prevented in an advantageous manner. Take into account the measures of the invention the fact that the current conducted through the bulk material always tends to take the path of least resistance, as has already been recognized and expressed in publications. The overheating of the bulk material in some places, namely in the vicinity of current threads of lower resistance with inadequate heating of adjacent material areas, can be avoided much better by the equalization with the measures according to the invention than with the complicated furnace construction of the known, resistance-heated furnace. There the side walls forming the furnace space would have to be arranged in such a way that the transverse dimension of the current path would be reduced with increasing distance from the electrode. This is the only way to improve the probability of a uniform current density over the entire cross section of the furnace. However, it is evidently easier to influence the current density by the arrangement of electrodes on the end walls of the furnace chamber, while the design and geometric shape of the side walls and the end walls holding the electrodes remain independent.

In an expedient further embodiment of the invention, the electrodes are attached to the most distant, preferably flat end walls of the furnace chamber, which is elongate in cross section. As a result, the furnace space can be designed not only in the simplest geometrical shapes but also with the formation of long current paths. Nevertheless, the installation of the furnace in an overall system and the use of commercially available materials is cheap and possible at low cost.

The electrodes can be made of graphite, metal or other suitable substances and, according to the invention, are expediently attached to one end wall one above the other and / or next to one another, the outlet preferably having two emptying openings with outlet cones which touch one another approximately below the center of the furnace space. In general, the device according to the invention is constructed in practice so that the front and side walls go up approximately vertically, so that the inlet is arranged at the top and the outlet at the bottom. In this case, bulk material will usually form a cone after the furnace space has been filled, so that a larger cross-sectional area would be present between the opposing pairs of electrodes in the case of a flat outlet surface in the middle of the furnace space. If, according to the above-mentioned measures of the invention, two discharge openings with outlet cones are arranged side by side in the manner described, the cross-sectional enlargement in the furnace filling in the middle of the furnace space caused by the pouring cone mentioned is compensated for, and the current density in the entire container advantageously remains for the current path flowing from one electrode to the opposite electrode is again the same.

According to the invention, the electrodes are therefore arranged, for example, one above the other on one and correspondingly also on the opposite end wall. In order to prevent the current from flowing through other neighboring electrodes instead of flowing directly into the heating material, even in difficult cases, it is expedient according to the invention if the electrodes are plates arranged above and / or next to one another in the shape of a blind. Conveniently, each electrode consists of a plate, which may be elongated in the horizontal direction, and the next electrode is arranged in a scale-like structure or as in the form of the individual leaves of a blind above or the next one underneath, whereby the actual distance from one electrode to the adjacent electrode also Advantage is increased. However, the above-described cross flow of the current through several electrode plates is thereby prevented. In this way, the current flowing from one electrode to the other is forced into the various current paths, even though, for example, the density of the bulk material is greater in the lower part of the furnace space and thus there is also better thermal conductivity of the bulk material in the lower region. The Venetian blind arrangement of the electrode plates allows the full use of the available wall area for the electrodes and forces the current along separate current paths between the respective pairs of electrodes.

To ensure the uniformity of the current flow even under unfavorable conditions, e.g. to ensure by different filling of the container, different density of the bulk material, grain distribution of the same, etc., it is particularly advantageous according to the invention if at least one electrode is provided with a current guide rail projecting into the furnace chamber. This preferably protrudes transversely out of the plate and thus into the bulk material at the end wall. It is particularly preferred to arrange such conductor rails in the upper region of the bulk material of lower density, loose filling and in particular in the presence of a pronounced cone of bulk. The current flow can namely be forced in the desired direction by these conductor rails and distributed individually in the desired manner for each individual case. The length, direction and size of the conductor rail naturally play an important role here, as will be explained below.

It is therefore advantageous if, in a further embodiment of the invention, the length and / or the position of the conductor rails protruding from the electrode plates is adjustable. It is also advantageous if the angle at which the conductor rails protrude from the electrode plates can be adjusted. For example, the adjustment of the angle and also the length of the conductor rail depends on the bulk material in question. Before a device according to the invention is put into operation, the optimum current ver division or guidance of the current paths can be set by appropriate setting of the conductor rails.

The arrangement and adjustment of the direction and length of these conductor rails make it possible according to the invention in a very simple manner to guide the current flow in the furnace space upwards into the pouring cone and also into the layers of the bulk material with a lower density. The attachment and design of these conductor rails is designed so that adjustment can be carried out according to individual needs during commissioning.

The arrangement of the current guide rails, possibly in conjunction with the louver-shaped arrangement of the electrode plates, further enables the simple geometric design of the container or the walls forming the furnace space. In this way, easy adaptation to often difficult installation conditions is possible. Furthermore, different sizes of the device with the same basic shape are possible due to more or less current carrying sections, which can be arranged one above the other by arranging several electrodes.

In the above-mentioned use of two emptying openings with outlet cones, for example, a rectangular or square shape instead of a round cone for the outlet pyramid stumps can be provided, so that a lining with high-temperature-resistant plates, which are also particularly wear-resistant, provide, in particular to the in Alumina ceramics, which are already customary in technology, are currently intended. This extremely wear-resistant and temperature-insensitive material is only supplied in certain standard formats and can be used with the device according to the invention in any type of device without the need for subsequent processing.

It goes without saying that the current strength is adjustable and can be regulated automatically. It is therefore expedient if each circuit has a three-phase thyristor control device for regulating the current and an isolating transformer for electrical isolation and voltage reduction. The device according to the invention can be operated with direct current, alternating current or three-phase current. When using direct current, a rectifier is also installed in each circuit, e.g. a three-phase rectifier.

It is also expedient according to the invention if the electrical energy introduced into the bulk material in the furnace space can be preset as a whole for each pair of electrodes and / or for all current paths. The desired degree of heating can thus be advantageously selected by specifying the energy to be introduced (in kilowatt hours). There is the possibility of a separate energy specification for each individual current path or a total energy value for all current paths together. As soon as the desired amount of electricity per lane in one case and / or per device as a whole in the other case has been initiated, the respective lane or the power supply of the device as a whole is switched off. The energy input is measured, for example, by a three-phase meter with a contact device and zero reset.

It can also be useful if, according to the invention, a stirrer and / or a spreading disc are provided in the furnace chamber. Then the introduction and distribution of the electrical current can be favored even if different grain sizes are present or the homogeneity of the bulk material to be heated is insufficient. The use of a spreading disc over the inlet creates z. B. an extremely uniform loading of the furnace chamber without the formation of the pouring cone described above, so that the related separations between coarse and fine grains are also eliminated.

If, in a further embodiment of the invention, it is provided that the walls forming the furnace space are flat and placed and supported on weighing devices, the device according to the invention can be used directly as a weighing container. In the case of continuous operation, the monitoring of the furnace weight can be used to control the flow rate and / or to control the power supply.

• Figur 1 die Vorrichtung zum Erhitzen im Querschnitt,
• Figur 1a eine Draufsicht auf die Vorrichtung der Figur 1, die insofern eine Schnittansicht entlang der Linie A-B der Figur 1a darstellt,
• Figur 1b eine andere Querschnittsansicht der Vorrichtung nach Figur 1, und zwar entlang der Linie C-D in Figur 1a,
• Figur 2 schematisch eine ähnliche Bauform, bei welcher verstellbare Stromleitschienen mit unterschiedlicher Eintauchtiefe von der Seite gezeigt sind,
• Figur 2a die Ansicht in die Vorrichtung der Figur 2 von oben,
• Figur 3 wiederum schematisch die Vorrichtung ähnlicher Baugestalt, bei weicher am Auslauf Austragsgeräte und Regeleinrichtungen vorgesehen sind,
• Figur 4 eine weitere andere Gestaltung des Ofenraumes unter schematischer Darstellung der Vorrichtung,
• Figur 5 eine wiederum andere Modifikation der schematisch in ihren Umrissen dargestellten Vorrichtung,
• Figur 6 eine weitere andere Ausgestaltung der Vorrichtung mit am Einlauf vorgesehenem Streuteller und mit Austragseinrichtungen und
• Figur7 eine ähnlich aufgebaute Vorrichtung wie nach Figur 1, wobei jedoch die Lagerung der Vorrichtung auf einer Wiegeeinrichtung vorgesehen ist, mit Regeleinrichtungen.

Further advantages, features and possible uses of the present invention result from the following description of preferred exemplary embodiments in conjunction with the drawings. Show it:

• FIG. 1 shows the device for heating in cross section,
• FIG. 1a shows a top view of the device of FIG. 1, which in this respect represents a sectional view along the line AB of FIG. 1a,
• 1b shows another cross-sectional view of the device according to FIG. 1, specifically along the line CD in FIG. 1a,
• FIG. 2 schematically shows a similar design, in which adjustable conductor rails with different immersion depths are shown from the side,
• 2a shows the view into the device of FIG. 2 from above,
• FIG. 3 again shows schematically the device of a similar design, in which discharge devices and regulating devices are provided at the outlet,
• FIG. 4 shows another design of the furnace space with a schematic representation of the device,
• FIG. 5 shows yet another modification of the device shown schematically in its outline,
• Figure 6 shows another embodiment of the device with a spreading plate provided at the inlet and with discharge devices and
• Figure 7 shows a similarly constructed device as in Figure 1, but with the storage of the front Direction on a weighing device is provided with control devices.

1 shows the device for heating electrically conductive bulk material 1, the end walls 2, 3, the side walls 4, 5, the inlet 6 and the emptying openings 7, 8 with the outlet cones 9 being shown in connection with FIGS. 1a and 1b are. It goes without saying that the walls 2-5 forming the furnace chamber designated 10 have a steel skeleton with thermal insulation on the outside and heat-resistant insulating plates on the inside towards the furnace chamber 10. In the area of the outlet cone 9, the covering with ceramic tiles 11 can also be seen.

FIGS. 1 and 1b show the arrangement of five pairs of electrode plates 12 and 13, respectively, which are mechanically and electrically completely separate from one another and arranged one above the other in the shape of a blind. The upper three pairs of electrodes 12, 13 also have current-conducting rails 14 projecting into the furnace chamber 10 and projecting approximately perpendicularly into the bulk material 1 from the inclined electrode plates 12 and 13. The plates are at an angle of 30 to 45 ° to the vertical, while the conductor rails 14 protrude approximately perpendicularly from the plates. It can be seen that the upper conductor rail 14 facing the center 15 and thus the bulk material cone 16 is longer than the conductor rail arranged below it. The two lowest electrodes 12, 13 shown in FIG. 1 do not have conductor rails. In this embodiment it is ensured that the upper electrode plates 12, 13 provided with the conductor rails 14 are provided in a number divisible by three, so that three-phase operation is preferably provided here. The electrical connections 17 are shown schematically and are located on brackets 18 behind the electrode plates 12, 13 and allow the supply of the current or the connection to the respective voltage of the electrical lines RST shown in FIG. 1, each with an upstream alternating current regulator 19 and transformer 20.

From Figure 1b it can clearly be seen that a plurality of current guide rails 14 are arranged next to one another at a distance on an electrode plate 12 and that the outlet 7 is closed at the bottom with a closure flap 21 which is opened or closed via the hydraulic or pneumatic cylinder 22.

A device of the shape according to FIG. 1 is shown schematically in FIG. 2, and the special feature - also in connection with FIG. 2a - consists in the adjustability of the current guide rails 14 protruding from the electrode plates. In FIG. 2, three levels of electrode plates 12 and / or 13, and here the conductor rails 14 protrude in different lengths approximately in the horizontal direction. In the uppermost level A, the conductor rail 14 protrudes furthest towards the center 15, while in the lowest plane C the distance between the two conductor rails 14 projecting into the bulk material 1 is greatest. As a result, the outermost end protrudes farthest backward in this plane C. With dashed lines it is shown that in all three levels A, B and C, the current guide rails 14 can project equally far towards the center 15 of the furnace chamber 10, depending on the desired position.

In FIG. 2a, the connecting lines R, S and T are again shown, which lead to the individual electrodes (not shown) and thus also to the conductor rails 14. According to FIG. 2a, one looks into the furnace chamber 10 from above and therefore only sees the upper conductor rails 14 within the walls 2-5 with the spacing of the front ends of the same, which should be the same in this plane A, the uppermost plane. Dashed lines show plane B and the dashed lines shown in dashed lines on the outside show the conductor rails 14 inserted in plane C. Correspondingly, the conductor rails according to planes B and C protrude backwards or outwards from the furnace chamber 10, it being assumed here that in each level A, B and C three conductor rails, for level A z. B. A1, A2 and A3 are provided.

FIG. 3 again shows a container shape similar to that of FIGS. 1 and 2, and the electrodes 12, 13 are shown schematically as plates.

In this embodiment, vibrating troughs 23 are provided as discharge devices under the discharge openings 7 and 8, so that after heating, the bulk material falls onto a conveyor according to arrows 24 after leaving the discharge openings 7, 8. Here, the quantity of the bulk material conveyed per unit of time can be scanned by the conveyor belt scale 26 and fed to a controller 28 via line 27. Depending on the selected priority (selected temperature or throughput quantity), the throughput quantity of the bulk material conveyed by the vibrating troughs 23 - or generally the discharge devices - according to arrow 24 or the heating output of the current regulator 42 can be regulated via the regulator 28. Until the maximum or maximum output is reached, the heating output can also be regulated proportionally to the throughput. A control signal is passed through the electrical line 30 to the current regulators 42; how the control commands are passed to the vibrating channels 23 via line 29.

FIG. 4 shows another form of the furnace chamber 10, in which the amount of electricity can be adapted to the respective amount of material in the relevant plane. The stated percentages from 10% from bottom to 40% represent the distribution of the current flow z. B. from the right electrodes 13 to the left electrodes 12. This distribution should also correspond to the volume of the material 1 arranged in between in the respective layer or plane, with a particular one for each plane Current path is provided in the manner described above.

FIG. 5 shows a further different embodiment of a container, in which the electrode plates 12 are only indicated schematically at the edge. This two-cone or double pyramid shape of the furnace chamber 10 here serves to avoid dead space due to the pouring cone, which is largely reduced here.

A complete avoidance of a pouring cone is achieved with the embodiment according to FIG. 6, in which a spreading disc 31 is driven by a motor 32 and is arranged with the furnace space 10 approximately in the area of the inlet 6, so that the bulk material falling from the conveyor 33 to the left according to arrow 34 through the spreading plate 31 passes through approximately according to the arrows 35 and then causes the furnace chamber 10 to be filled without a pouring cone. Like the container according to FIGS. 4 and 5, the container according to FIG. 6 has only a single emptying opening at the bottom, and the bulk material can be removed after heating, for example with the removal belt 36 according to FIG. 6.

Finally, FIG. 7 shows a container shape similar to FIG. 1, but the entire device is supported on pressure measuring cells 37 in such a way that such an oven can be used directly as a scale.

In the case of continuous operation, the monitoring of the furnace weight can be used to control the flow rate and / or to control the power supply. The pressure load cells 37, from which the signals can be sent to the balance 38, can be seen in FIG. From there, there is a signal via line a ₁ for changing the quantity of material that is fed in, ie for controlling the throughput quantity. Additionally or alternatively, a control signal can go via line b to the electric generator 39, which controls the power supply via lines 40 (phases RST). Furthermore, a control signal can be passed through line c ₁ to the discharge device 41, so that the discharge quantity can be controlled here.

The device can also be characterized in that a continuously controllable discharge device is provided, the output of which can be matched to the pre-adjustable heating output. In another alternative, the device can be characterized in that a control device for the heating power, which is applied by a heating device, or for the electrical energy introduced, can be tuned to the setting of the controllable discharge device. In other words, a continuously controllable discharge device and a control device for the introduced electrical energy can be provided in the device according to the invention, the discharge and control devices being mutually coordinated.

Depending on the product quality and the task, it may be appropriate to provide either the continuously adjustable discharge device or the control device for the electrical energy introduced. Do you want e.g. maintaining a very constant temperature, then the throughput can be controlled so that all the discharged material has the desired temperature.

Claims (9)

1. Apparatus for the direct heating of electrically conductive bulk materials in a furnace chamber (10) utilising the electrical heating resistance of the bulk material (1), comprising an inlet (6), an outlet (7-9) and, arranged therebetween and laterally defining the furnace chamber (10), pairs of mutually oppositely disposed side walls (2-5), and at least two arrangements, which are disposed in superposed relationship at different levels of the furnace chamber (10), each comprising at least one pair of electrodes (12, 13) which are disposed in opposite relationship at the same level and which are mounted to a respective pair of said walls (2-5) of the furnace chamber (10), characterised in that the pairs of electrodes (12, 13), which are arranged in superposed relationship, are so connected that the one pair of electrodes (12, 13) is respectively galvanically separated from the other pair of electrodes (12, 13).

2. Apparatus according to claim 1, characterised in that the furnace chamber (10) is of an elongate configuration in horizontal cross-section and is delimited by at least one pair of horizontally longer side walls (4, 5) and at least one pair of horizontally shorter end walls (2, 3) and that the electrodes (12, 13) are mounted to the preferably flat end walls (2, 3) which are furthest away from each other.

3. Apparatus according to claim 1 or claim 2, characterised in that the outlet has two emptying openings (7, 8) with outlet cones (10) which meet each other approximately below the middle (15) of the furnace chamber (10).

4. Apparatus according to one of claims 1 to 3, characterised in that the electrodes (12, 13) are plates which are arranged in superposed and/or juxtaposed relationship in a shutter-like configuration.

5. Apparatus according to one of claims 1 to 4, characterised in that at least one electrode (12, 13) is provided with a current conductor bar (14) which projects into the furnace chamber (10).

6. Apparatus according to one of claims 1 to 5, characterised in that the length and/or the position of the current conductor bars (14) which project from the electrode plates (12, 13) is adjustable (Figures 2 and 2a).

7. Apparatus according to one of claims 1 to 6, characterised in that the electrical energy which is introduced into the bulk material (1) in the furnace chamber (10) is adjustable for each pair of electrodes (12, 13) and/or for all current paths in general.

8. Apparatus according to one of claims 1 to 7, characterised in that an agitator mechanism is arranged in the furnace chamber (10) and/or a distributor plate (31) is disposed at the inlet (6) of the apparatus.

9. Apparatus according to one of claims 1 to 8, characterised in that the walls (2-5) forming the furnace chamber (10) are flat and are supported and mounted on weighing means (37) (Figure 7).

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